OLED panels, which rely on OLED technology to generate light, offer many advantages for general lighting and display purposes. They are efficient in terms of light output for power consumed. They are low voltage which helps avoid potential electrical shocks, less prone to sparking in potentially explosive environments, and they reduce loads in the supporting electrical system. The spectrum of emitted light can be varied using appropriate internal designs. They produce little or no UV or IR light. They are instant on; that is, they emit light immediately whenever electrical power is supplied. OLED light sources are inherently flat area light sources. They offer several advantages over LED panels. They can be made even thinner (for example, less than 1 mm thick) and they produce less heat under normal operating conditions. However, OLED lifetimes can be an issue. Both LED and OLED panels can be made on flexible or curved substrates even though OLED is preferred for these types of applications. In summary, OLED panels can be useful for lighting and display applications. They are efficient, low voltage, cool to the touch, and are thin. Luminaires (a complete unit with a light source (i.e. a lamp) and a supporting part (i.e. a lamp-holder) that provides light and illumination) can be designed to utilize OLED panels as the light sources. Displays using OLED panels can either be direct, for example, the OLED panel contains individually controlled Red, Green and Blue (RGB) subpixels; Red, Green, Blue and White (RGBW) subpixels; individually controlled White subpixels with a color filter array or individually controlled Blue subpixels with a color conversion array; or indirect, for example, the OLED panel is used as a White backlight for an LCD panel used for RGB display.
In the lighting industry, luminaire design is often of critical importance. Besides addressing general or specific illumination needs, luminaires become part of the architectural environment. It would be very desirable to design luminaires that take advantage of some of the unique physical characteristics of OLEDs that differ from other light sources such as LED. The same considerations can also be applied to display applications.
Generally speaking, an OLED panel for use in a luminaire or a display would have at least three parts: an OLED substrate or support, an OLED light-emitting unit, and electrical connections which provide power to the internal OLED electrodes from an external source. An OLED light-emitting unit would have at least one organic electroluminescent layer between two electrodes on a substrate and would be encapsulated to protect the electroluminescent layer(s) from air and/or water. Typically, the OLED panel would have a central emissive area (continuous for lighting applications or subpixels for direct display applications) surrounded by non-emitting borders. Electrode contact pads, which are connected to the internal electrodes, are often located in these non-emitting border areas on the same face of the substrate as the electroluminescent layers.
For some luminaire designs, it would be desirable to use an OLED panel as a light source where the OLED panel has a pass-through hole. In such cases, the OLED lighting panel would have at least one hole or opening that is large enough to allow objects behind the panel to be viewed through the hole. Alternatively, the pass-through hole is large enough so that a solid element can pass through the hole. In both cases, the pass-through hole does not affect light emission in the surrounding area of the panel. The pass-through hole would be entirely within the central emission area of the OLED panel and is surrounded on all sides by a continuous and uninterrupted emitting area of the OLED panel. The space within the border of the pass-through hole is entirely empty; that is, there is no part of the OLED panel that exists within the hole. It is not merely a transparent and non-emitting area within the central emission area of the OLED panel. A pass-through hole could also be referred to as a through-hole, thru-hole or clearance hole, all of which are equivalent terms.
The OLED panel with a pass-through hole could also be a pixelated image display. In this case, the pass-through hole would be within the central display area of the OLED and is surrounded on all sides by a continuous and uninterrupted display area of the OLED panel. In such cases, the OLED display panel would have at least one hole or opening that is large enough to allow objects behind the panel to be viewed through the hole. Alternatively, the pass-through hole is large enough so that a solid element can pass through the hole.
In some designs, the pass-through hole is large enough that objects behind the panel are clearly visible. It is often not necessary that an entire object must be viewed, but only that it is sufficiently viewed to be detectable. However, the exact size of the pass-through hole needed to allow visibility of objects depends on many factors.
Firstly, since the light from the object (whose intensity is inversely proportional to the distance from the object) must pass through the hole, it is clear that the hole must be large enough to allow a sufficient amount of light from the object to pass to be viewable. This situation is complicated by the surface of the OLED panel which also emits light towards the viewer, thus partially diluting the light coming from the object.
Secondly, there is a problem related to the parallax effect when viewing through a hole. For example, consider the schematic diagram in FIG. 1A where P is the viewer, O is the optical axis of viewing, s is the distance between the hole and the viewer, f is the distance between the hole and the object, d is the total distance between the viewer and object, H is the size of the hole opening and qd represents the viewable size of the object that lies in plane S.
FIG. 1B illustrates the problem of viewing objects through a hole opening H which is very small, such as a pinhole. Assuming that the viewer P is as least the same distance in front of the hole as the distance of an object from the back of the hole, solid sightlines a, coming from the edge of an object, will not be in the field of view to the viewer P. Dotted sightlines b, also coming from the edge of the object but would be in the view of field to the viewer P, are blocked. Dashed sightlines c, coming from the viewer P through the hole opening H, will only subtend a limited part qd of the object. In this case, this subtended viewing area may not be enough to visibly detect the object through opening H.
FIG. 1C illustrates a similar situation where the hole opening H is large; in this example, at least as big as the object to be viewed through the hole. Assuming again that the viewer P is as least the same distance in front of the hole as the distance of an object from the back of the hole, solid sightlines a, coming from the edge of an object, will no longer exhibit any parallax issues. Dotted sightlines b, also coming from the edge of the object will be in the field of view to the viewer P. Sightlines c, coming from the viewer P through the hole opening H, will subtend over an area greater than the object. In this case, the object should be viewable through opening H. Typically, for OLED panels used as lighting, the distance s between the viewer and panel would generally in the range of multiple meters and the distance f between the object and the back of the panel would be typically be the same or less than the distance s and often significantly less. In such situations, it is easy to see that the size H of the pass-through hole would need to be relatively large in order to have a significant viewing size of the object. Even in the case where the OLED panel is a display and the position of the viewer is much closer (typically 0.1-0.5 meter) to the hole, the size of the hole would still need to be much larger than the pixels in order for an object to be visible. The depth or thickness of the hole can impact the hole size needed for visibility of objects; however, OLED panels and housings are generally thin enough not be a significant consideration in this regard.
In some designs, there can be a solid element that extends through the pass-through hole or at least partially within the pass-through hole. In such cases, the OLED panel with the pass-through and the solid element together form a single integral unit. In some designs, the presence of the solid element is strictly decorative and the OLED panel/solid element unit provides architectural interest. In other designs, the solid element provides a function such as mechanical support or space to conceal electrical wires.
U.S. Pat. No. 8,053,977 describes OLEDs for phototherapy with pass-through perforations that allow fluids and/or heat to escape when onto human skin. The holes appear to be small (a diameter of 40 μm is given as an example) relative to the overall size of the OLED. This reference also describes a method where the deposition of electrode/organic/electrode layers is prevented (presumably via masking) near the perforation area, followed by encapsulation over everything, followed by perforation.
CN104576709 describes a wearable OLED display (i.e. wristwatch) where the pixels have ventilation holes in order to make it breathable. The holes are small (80 microns). This reference describes the formation of an OLED (anode/organic/cathodes/SiN protective layer) uniformly over a flexible base, forms the holes, then encapsulates. The holes are cone shaped with sloping sides (small at the front of the substrate then larger towards the back).
In both of the above references, the holes in the OLED are very small and are sized to allow for air and fluid exchange when the OLED is placed next to the skin. The holes as described would not large enough to view the skin through the OLED. In both of these references, the internal structure of the OLED is modified prior to encapsulation to allow the formation of the pinhole without breaking a pre-existing encapsulation.
It is the object of the invention to provide a method for the re-encapsulation of the cut edges of a pass-through hole when the pass-through hole is formed in an OLED that was already fully encapsulated. When a pass-through hole is formed in the emissive area of an OLED, the edges of the moisture- and oxygen-sensitive OLED layers will be exposed to the atmosphere along the side walls of the pass-through hole. It is well known that moisture and oxygen can travel laterally through thin organic layers if the edge of the layer is left exposed. For cost and availability considerations, it would be advantageous to begin with an existing fully encapsulated OLED and then form the pass-through hole. However, it is necessary to re-establish the encapsulation along the newly formed cut edges along the side walls of the pass-through hole of the OLED panel in order to maintain its useful lifetime. An OLED panel with a pass-through hole that allows visibility through the opening is useful because it enables unique designs of luminaires or displays.
U.S. Pat. Nos. 9,343,695 and 9,818,977 describes OLEDs with light-emitting areas that can be made in any desired shape by cutting or etching the substrate and OLED layers in at least two steps. The formation of pass-through holes is not disclosed. Side edge encapsulation of vertical cuts made after encapsulation is discussed. For example, these references disclose that sealing polymers, with or without moisture-absorbent materials, or metal may be applied to the cut edges to reestablish the encapsulation. However, it has proven difficult and unreliable to apply a sufficient amount of sealing material directly to a thin cut edge to provide sufficient protection against moisture and oxygen.
U.S. Pat. No. 9,219,245 describes where an OLED on top of a substrate is encapsulated by covering the OLED with a sealing substrate, larger than the OLED substrate, with an adhesive and folding the edges of the sealing substrate over the edges of the OLED substrate. There may be a filler or moisture-absorbing materials or both in the space between the side and back edges of the OLED substrate where it meets the sealing substrate. The disclosed method relates only to the straight outside edges of the substrate which are already encapsulated.
U.S. Pat. No. 8,253,329 describes a method of encapsulating OLEDs where the edges of an impermeable backsheet (substrate) extend past the edges of emitting portion of the OLED and are folded over the edges of the light-emitting portions to come into contact with a top barrier sheet over the emitting portions, thus forming the sides of the encapsulation package. There may be an adhesive between the edge of the emitting portions and the top of the barrier sheet and the folded backsheet. The adhesive may contain moisture absorbing materials. This method is not applicable for re-encapsulation of a newly formed pass-through hole.
U.S. Pat. No. 9,831,467 describes the encapsulation of multiple OLED units on a single flexible substrate by applying thin-film encapsulation of a first inorganic layer, intermediate organic layer and second inorganic layer uniformly across the substrate, removing the thin-film encapsulation from the substrate along the edges and/or around where the substrate is to be cut and reapplying thin-film encapsulation to the areas where it has been removed. The second thin-film encapsulation prevents the organic layer of the first thin-film encapsulation in each separated OLED device from being exposed after cutting. However, this requires removal of materials in certain areas which adds manufacturing costs and creates the possibility of contamination during the removal process. In addition, the OLED panel becomes thicker since there will be two encapsulation layers over the bulk of the device.
KR10-0635576 describes a method of further protecting the side edges of existing encapsulation by applying a protective film over the seam where a top encapsulation meets the substrate.
U.S. Pat. No. 9,761,837 describes the formation of multiple OLED units on a substrate, then forming a common thin-film encapsulation of a first inorganic layer, intermediate organic layer and second inorganic layer, followed by a common protective layer. The substrate is then cut between the OLED units in an area where the second inorganic layer is in contact with the substrate to form individual encapsulated OLED devices.
CN107863453A describes the encapsulation of an OLED using a metal foil along the side edge which is ultrasonically welded to a metal foil over the non-emitting face of the OLED.
U.S. Pat. No. 6,998,648 describes encapsulated OLEDs where a cover with a getter region is bonded to a substrate using a pressure sensitive UV curable adhesive.
EP0577276A2, EP1270675A1, US20050255285, US20060223903 and WO2017/218500 all describe suitable getter or desiccant materials and formulations for use in encapsulation.